Engineering Explained: F-150 better than Cybertruck for towing duty (over distance)

[ajdelange]

`-how to get my 14k minimalist kit 100 miles away and 1 mile up. But I totally get it.

That's a lot of trailer. It is 14000/2.2 = 6363.6 kg worth of trailer. Let's look at the easy part first: getting that 1 mile up. A mile is 1600 meters. The acceleration due to gravity is 9.8 m/sec^2 so to get that trailer up 1 mile you will have to put at minimum 9.8*6363.6*1600 = 9.97812e+07 joules of energy into it. A watt hour is watt for 3600 seconds i.e. 3600 joules so this job means 9.97812e+07 /3600 = 27717 kWh (from a, perhaps, 200 kWh battery).

Now the rest of the job of calculating how much energy is required is much trickier. The math is pretty straight forward. It is summarized at
https://www.cybertruckownersclub.com/forum/threads/cybertruck-towing-range.334/page-2
The problem isn't the math. It's knowing what numbers to put into it. For example with regen we just calculated that going up a mile requires drawing 27717 kWh from the battery and that coming down we should recoup much of that but we don't know what "much" is numericall (80% ?). And we don't know what the drag of the trailer is relative to the vehicle. Thus I have taken the approach of estimating that trailer drag, relative to truck drag is the ratio of their masses to the 2/3 power (justified by ratio of volume to surface area) and made other equally shaky assumptions 80% regen recovery) to prepare the chart in that post. It suggests that towing a 14,000 pound trailer up a 1% (1 mile in 100 miles) will result in reduction of range to 21% of the truck's EPA rated range i.e. it will result in a practical range of about 100 miles. Now we note that you don't charge the battery fully and then discharge it fully before recharging. Running between 10% and 90% i.e. about 80% of usable capacity is more reasonable and so your practical range with a trailer this big is about 80 miles. Also be aware that historical data collected from the Tesla fleet shows that drivers achieve between 86 (winter) and 93 (summer) % of the EPA range so at the higher end range will probably be reduced by another 7 % to around 75 miles. Also be aware that anything that increases consumption such as underinflated tires and, a big one, water on the road surface, will reduce range further.

Be aware that my chart is not going to give you an accurate prediction but is rather intended to give you a general idea of how grade and weight interact. Nevertheless my conclusion is that the CyberTruck is not the truck for pulling something as heavy as 14,000 pounds unless you can and are willing to recharge every 80 - 100 miles. You will have to decide whether this is acceptable or not.

I tow heavy locally with 60 mile round trips.

That might work for you.

Instead of spending 50 bucks filling up I would like to spend 25 on electricity. Or less.

We can WAG this (but it will be a WAG). The range estimate for the CT plus 14000 lb trailer is 80 - 100 miles.The battery in the CT is going to be about 200 kWh and you are going to use a good part of that on a 60 mile trip. Thus your fill up cost is going to be a good part of 200 times the cost of a kWh of electricity. On average in the US that's 13 cents at home so $26 if you charge at home. At Tesla Super Chargers the average cost is about twice this so $52 is approximately what you will be paying if you charge on the road at SC's. If you have to use non Tesla chargers the cost may go up by another factor of as much as 2 which means that you will be paying more than you would for gas.

Also I’d like to use regen braking advantages when towing.

Regen charges the battery and there are limits as to how fast the battery can accept charge, even without a trailer. It stands to reason that if you are towing something which triples the total mass of the system that regen is going to be limited. This will result in a dramatic reduction in range, especially in hilly country. Were I contemplating towing something this heavy with the CT this is something I would look at very closely.

i wish he would talk about in the video electrical energy generation efficiency, transmission efficiency, the difference in pollution, and the cost of electric fill up versus ICE.

There are hundreds of videos and articles that go into this.

And what each trip to the mountains does to the environment.

If you charge from a clean source (nuclear, solar, wind, hydro) it has no impact other than the particulates from the tires. If you charge from a coal burning plant that's obviously not the case but it's still less than using a diesel vehicle.

Towing 14k fifth wheels Is pretty fancy.

It's definitely operating close to the boundaries of the envelope. I'd be extremely cautious.

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[Cougs]

NEWS:

Musk: Production Cybertruck Will Look Better Than Concept and Feature Advanced Towing Software

 

[Dids]

Cyber truck can tow this for me.
https://taxaoutdoors.com/camper-trailers/mantis/

 

[Keeney]

No. This is voodoo math. Let's take CT out of comparison and substitute it for a diesel identical to the gas ICE.... ( they both have unloaded range that is identical)

The nuances of various engines (and electric motors) having differing efficiencies under differing loads might be a factor, but not the dominant one.

A much larger factor is the difference in aerodynamics. The CT has much better aerodynamics than the typical pickup when NOT pulling the trailer. So it needs/has less energy capacity to start with (for the same range). But when pulling a large trailer, the drag is dominated by the trailer.

 

[ajdelange]

I keep trying to get people to understand that the basic concept is quite simple. It takes energy to move a truck and it takes energy to move a trailer. If it takes twice as much energy to move the trailer a mile as it takes to move the truck alone then to move the coupled pair takes three times as much energy as would be required for the truck alone and the range the pair can be towed is going to be 1/3 of the truck's range. The efficiency of generation of traction power does not come into it. Anything that effects the relative energy required to move the two vehicles (aerodynamic drag, weight, wheel bearing friction) does.

 

[Dids]

Yes "if" it takes 3 times as much energy.... what I'm been trying to say is you cannot determine how much energy it takes to move a vehicle by saying 3x the weight and drag means 3x the energy. If this was true then diesel rigs would not tow longer distances with the same energy over gas rigs, yet in the real world this is true. The difference is torque produced by the energy. Think of torque as a lever, a power plant with a longer lever is effected less by increasing the load than a power plant with a shorter lever.

 

[ajdelange]

what I'm been trying to say is you cannot determine how much energy it takes to move a vehicle by saying 3x the weight and drag means 3x the energy.

If you can say that weight is 3x (which you can) and if you can say that drag is 3x (which you can't but you can measure drag if the trailer coupler is a load cell) then you can say the energy used is triple because ∫3*f(x)dx = 3*∫f(x)dx is the energy required to move along the x axis when the force (toque/wheel radius) is f(x) at point x. This pertains to both the force required to overcome inertia and pure drag related forces. What you cannot do with better than rough accuracy is assume, as I do for my rough calculations, that drag force is propotional to the 2/3 power of weight.

If this was true then diesel rigs would not tow longer distances with the same energy over gas rigs, yet in the real world this is true. The difference is torque produced by the energy.

Diesels use exactly as much energy, ceteris paribus, to tow a trailer as gasoline engines. But a diesel need produce a bit less total energy and pollution than a gas engine because the specific energy of diesel fuel is 37.18 GJ/m^3 as opposed to gasoline's 33.9 and diesel engines are 10 or more percent more efficient than gasoline ones. IOW to deliver 100 J to the wheels a gasoline car may have to produce and waste between 185 and 400 J as heat whereas a diesel will waste as little as 122. And, of course, a BEV as little as 11.

Think of torque as a lever, a power plant with a longer lever is effected less by increasing the load than a power plant with a shorter lever.

I can only think of torque as what it is: is the product of force by the length of the arm (the radius of the wheel). Thus the integral of thrust over distance in the first paragraph can be replaced by the integral of torque over wheel angular position if desired but the answer is the same. The source of the torque or thrust has nothing to do with it and the amount of torque required to move the rig at a certain velocity over a certain section of road does not depend on whether the energy source is petrol, diesel, fuel cell, battery or rubber band.

 

[Mule Ferguson]

I wonder why the Tesla Semi is selling well. The companies know what is better.

https://www.businessinsider.com/companies-that-ordered-tesla-semi-2017-12

 

[ajdelange]

The only advantage of diesel is that the energy needed at the wheels to move a load comes from gas tank that is smaller and lighter than the equivalent battery. But as that doesn't matter for short and medium range hauling it makes more sense to use a battery and reap all the benefits it provides mainly appreciably lower operation (fuel and maintenance) costs. And you can brag about how much you care about the planet too.

 

[Dids]

I guess Archimedes was wrong.

 

[ajdelange]

No, he was right. What's wrong is the way you interpret what he said. You seem to grasp the fact that one need only apply 1 pound of force to the end of a lever 1000' long (from the pivot) to lift a 1000 pound weight 1' from the pivot. What you have not perhaps thought through is that to lift a weight 1 foot you must do 1000 foot pounds of work on it. It doesn't matter where you do it. The required energy is the same. Thus Hercules at the weight would have to apply 1000 pounds force and lift 1 foot. Archimedes would only have to apply 1 pound but would have to depress his end of the lever 1000 feet. Same amount of work: 1000 foot pounds.

But this has nothing to do with the problem under discussion. A 100 hp engine delivers the same torque at rated speed whether it be steam, gasoline, diesel, stirling or electric.

 

[Dids]

So what you just said... Archimedes gets to go 1000 ft and Hercules gets to go a foot for the same amount of energy. ?

 

[ajdelange]

The First Law of thermodynamics demands that energy be conserved. That means that a joule from a diesel engine will move a trailer with a given energy per unit distance requirement as far and no farther than any other type of engine. To suggest otherwise asks people to reject the First Law. That's going to be a hard sell. If you are trying to say what it appears you are that shows a disconnect from Newtonian mechanics so profound that there is little chance that it can be resolved here. Nor is this really the place to try do it.

 

[Dids]

The First Law of thermodynamics demands that energy be conserved. That means that a joule from a diesel engine will move a trailer with a given energy per unit distance requirement as far and no farther than any other type of engine. To suggest otherwise asks people to reject the First Law. That's going to be a hard sell. If you are trying to say what it appears you are that shows a disconnect from Newtonian mechanics so profound that there is little chance that it can be resolved here. Nor is this really the place to try do it.

No I am not trying to say that... The Hercules thing was a joke. But there are people on here trying to say that the range is reduced more for electric than it is for gas. In reality towing the same trailer reduces the range equally for gas or electric with a slightly less reduction in range for electric. This is due to the maximum torque available over the operating range. The only real difference is the speed of filling up the tank.

 

[Keeney]

No I am not trying to say that... But there are people on here trying to say that the range is reduced more for electric than it is for gas. ...

It has nothing to do with electric vs gas vs diesel. It has to do with the difference in aerodynamic drag of the shape of the CT vs the shape of a conventional shaped pickup (presuming their weight to be similar). If they had the same drag and weight, then towing the same trailer would result in the same range reduction.

But they don't. The CT has significantly less drag to start with.

Its counter-intuitive, but adding the trailer to the CT is a larger percentage increase in drag as compared to the percentage increase of adding the trailer to the conventional shaped pickup. Which means a larger percentage decrease in range.